Ryou Marufuji

Ryo is the best duelist in Duel Academy. Unlike his little brother (Sho Marufuji) he excels in all dueling forms. He often studies the dueling format with all duelists, and never underestimating his opponent. He uses some of the most powerful Machine Type monsters in the game. He was also undefeated in Duel Academy, hence the nickname "Kaiser".

Spoiler, click to viewclick to hide

(until his first loss ever, in season 2, to Aster Phoenix)

In the manga, Ryo is an exchange student to the U.S who returns to Duel Academy with two attendants.